log2

SYNOPSIS
#include <math.h>
double log2(double x);
float log2f(float x);
long double log2l(long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
log2(), log2f(), log2l():
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
DESCRIPTION
The log2() function returns the base 2 logarithm of x.
RETURN VALUE
On success, these functions return the base 2 logarithm of x.
For special cases, including where x is 0, 1, negative, infinity, or
NaN, see log(3).
ERRORS
See math_error(7) for information on how to determine whether an error
has occurred when calling these functions.
For a discussion of the errors that can occur for these functions, see
log(3).
VERSIONS
These functions first appeared in glibc in version 2.1.
CONFORMING TO
C99, POSIX.1-2001. The variant returning double also conforms to SVr4,
4.3BSD.
SEE ALSO
cbrt(3), clog2(3), log(3), log10(3), sqrt(3)
COLOPHON
This page is part of release 3.54 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
2010-09-12 LOG2(3)